The study investigates to what extent English as a second language (ESL) learners develop explicit and automatised explicit knowledge of two target-forms (third person singular 's' and future conditional if-clause) after input and output based instruction and whether learning effects differ depending on the target forms. The study follows a pre-test--post-test design. Seventy-two intermediate level ESL learners from three intact classes were randomly assigned to two experimental groups (input and output) and one control group. The experimental groups completed a pre-test and received relevant instructional treatment: the input group received processing instruction that did not involve any production of output, whereas the output group received output based instruction. Immediately after the instructional treatment, the experimental groups took a post-test and after two weeks, a delayed post-test. The control group took the same tests without receiving any instructional treatment. An error correction test and an oral narrative production test were used to measure explicit and automatised explicit knowledge, respectively. The results showed that both the input and output groups outperformed the control group in developing explicit knowledge of the target forms, and the output group outperformed the input group in developing automatised explicit knowledge of both target forms.